OK I found the answer to my own question.
The command is as follows:
username billybob autocommand any_command_here
The will only allow the user in question to run that one command. As soon as the command finishes, the user is logged out.
You could also use this command to call a predefined menu of commands:
username billybob autocommand menu my_custom_menu
To disable the automatic disconnection after the command is run:
username billybob nohangup autocommand menu my_custom_menu
Hope that helps someone someday....
